Thru tubing retrievable bridge plugs provide a means of temporarily plugging selected sections of a well, without the need for pulling production tubing. Avoidance of the need to pull the production tubing dramatically reduces costs associated with plugging particular sections of a well. Different sections of a well might need to be plugged because of, for example, water breakthrough, gas production, etc. Retrievable bridge plugs are also run to plug certain sections of a well in order to test different fluids flowing into the well at that location or above that location from shallower zones within the wellbore. Such bridge plugs generally include a lower valve which provides a seal, blanking off a section of mandrel so that a packer element, also contained within the retrievable bridge plug, can be inflated. The packing element provides for the plugging off of the selected sections of the well. The construction and use of a conventional bridge plug is considered known to one of ordinary skill in the art. Such bridge plugs are commercially available from many sources including Baker Oil Tools, Houston, Tex. (Product Nos. 340-10 and 330-72).
The above-identified drawbacks of the prior art are overcome, or alleviated, by the intelligent bridge plug system of the invention.
The present invention avails itself of the benefits evident in conventional retrievable bridge plugs and further provides a method and apparatus for accurately setting the inflation pressure of a retrievable bridge plug and verification of that setting. The apparatus of the invention is a thru tubing bridge plug having downhole instrumentation and employing an electric wireline setting tool such as that disclosed in co-pending U.S. Ser. No. 60/123,306, filed Mar. 5, 1999, the entire contents of which is incorporated herein by reference. The device further comprises several sections of a retrievable bridge plug and several downhole sensors. The sensors are worked into the tool preferably in a sensor module which is a part of the retrievable bridge plug assembly. The sensor module is located in different sections of the tool for different embodiments as disclosed hereinbelow. The tool of the invention preferably measures element inflation pressure, temperature inside the packer and the annulus temperature as well as pressure uphole of (above) and downhole of (below) the packer. These parameters of the well may be used to ensure a proper setting of the inflatable element and thereby ensure that the bridge plug operates as intended. The invention provides a superior advantage over the prior art for many reasons including that the temperature of the inflation fluid is nearly always cooler than the temperature downhole. If a packer is fully inflated with relatively cooler fluid, the thermal expansion of that fluid subsequent to filling could rupture the element. Such occurrence could be problematic and would preferably be avoided. The present invention provides the means to avoid such a condition and also will provide a high degree of confidence that the inflatable element is properly inflated every time the bridge plug is employed.
It is also important to note that one of the key points in measuring pressure below the bridge plug is to determine how the well is responding to the plug. This is an important benefit of the invention not heretofore available; comparing pressure above the plug with pressure below the plug which provides information about whether or not a zone has been effectively shut off and whether or not the packer has achieved a good seal. The existence of leaking through the casing or through fractures in the formation, etc. would be identified by comparing the above and below pressure. Moreover, the comparison indicated above provides information about whether or not pressure below a plug is being adversely affected by other wells in a situation where production wells and injection wells are operating in the same field. Furthermore, by monitoring all three of above the plug pressure, below the plug pressure and element inflation pressure verification can be obtained that the inflation pressure ratings for the element being employed have not been exceeded.